Injector cleaning system based on pressure decay

ABSTRACT

An injector cleaning system for use with an exhaust treatment device is disclosed. The injector cleaning system may have a supply of injection fluid and an injector configured to receive and inject the injection fluid. The injector cleaning system may also have a pressure sensor associated with the injector to generate a signal indicative of the pressure of the injection fluid supplied to the injector. The injector cleaning system may further have a controller in communication with the injector and the pressure sensor. The controller may be configured to determine a pressure decay rate of injection fluid supplied to the injector during a normal injection event based on the signal. The controller may be further configured to compare the determined pressure decay rate to an expected pressure decay rate, and supply cleaning fluid to the injector based on the comparison.

TECHNICAL FIELD

The present disclosure is directed to an injector cleaning system and,more particularly, to an injector cleaning system that cleans aninjector based on a pressure decay.

BACKGROUND

Engines, including diesel engines, gasoline engines, gaseous fuelpowered engines, and other engines known in the art exhaust a complexmixture of air pollutants. These air pollutants include solid materialknown as particulate matter or soot. Due to increased attention on theenvironment, exhaust emission standards have become more stringent andthe amount of particulate matter emitted from an engine is regulateddepending on the type of engine, size of engine, and/or class of engine.

One method implemented by engine manufacturers to comply with theregulation of particulate matter exhausted to the environment has beento remove the particulate matter from the exhaust flow of an engine witha device called a particulate trap or diesel particulate filter. Aparticulate trap is a filter designed to trap particulate matter andtypically consists of a wire mesh or ceramic honeycomb medium. However,the use of the particulate trap for extended periods of time may causethe particulate matter to build up in the medium, thereby reducingfunctionality of the filter and subsequent engine performance.

The collected particulate matter may be removed from the filter througha process called regeneration. To initiate regeneration of the filter,the temperature of the particulate matter trapped within the filter mustbe elevated to a combustion threshold, at which the particulate matteris burned away. One way to elevate the temperature of the particulatematter is to inject a catalyst such as diesel fuel into the exhaust flowof the engine and ignite the injected fuel.

After the regeneration event, the supply of fuel is shut off. However,some fuel may remain within the fuel injector or the fuel lines thatdirect fuel to the injector. This remaining fuel, when subjected to theharsh conditions of the exhaust stream, may coke or be partially burned,leaving behind a solid residue that can restrict or even block the fuelinjector. In addition, it may be possible for particulate matter fromthe exhaust flow to enter and block the injector. For these reasons, itmay be necessary to periodically clean or purge the injector of fueland/or any built up residue or particulate matter between regenerationevents.

One method of cleaning a fuel injector is described in U. S. Pat. No.4,977,872 (the '872 patent) issued to Hartopp on Dec. 18, 1990.Specifically, the '872 patent discloses an injector cleaning/testingapparatus arranged to enable electrically actuated injectors to becleaned and tested while in situ on an engine. The apparatus isconnected to the fuel supply system of the engine, which feeds fuel anda cleaning fluid to each of the engine's injectors. During a cleaningcycle, the injectors are connected for normal operation by the vehicleinjector controls, and cleaning fluid is therefore injected into theengine so that it runs normally, the cleaning fluid also acting as fuelfor the engine as well as cleaning the injectors by its passagetherethrough.

Prior to or after a cleaning cycle, each fuel injector is individuallytested to ascertain whether flow characteristics of the fuel injectorare as required or if the cleaning operation was successful. To test theinjectors, fuel is pumped to the injectors and the pressure of the fuelsupply is measured. One of the injectors is then energized and openedfor a predetermined time of, say 2-3 seconds. During this time interval,fuel is passed through the injector and a pressure drop occurs in thefuel line to the injector. A pressure sensor records the pressure dropover this time interval and signals the pressure drop to an electroniccalculating means. The calculating means compares the recorded pressuredrop with a calibrated amount to give an output signal indicating theflow rate through the selected injector. The tests determine for theoperator which, if any, of the injectors is defective or inadequatelycleaned.

Although the apparatus of the '872 patent may allow for testing andcleaning of injectors and does so in situ, it still may be limited.Specifically, because the apparatus only tests injector performance whenmanually triggered to do so, there may be situations when the injectorscould be unknowingly operating sub-optimally such as between standardscheduled diagnostic/service events. In addition, because the apparatusonly checks the quality of a cleaning based on a technician's desire todo so, the quality checks may be periodically skipped or omittedaltogether, thereby allowing for a malfunctioning injector to continueperforming poorly. Further, because the apparatus of the '872 patentprovides only a single level of cleaning, severely clogged injectors maybe treated the same as injectors having only a slight restriction. Forthis reason, some injectors may be cleaned inadequately, while cleaningfluid may be unnecessarily wasted on other injectors.

The apparatus of the '872 patent may also be expensive and interruptive.That is, because the cleaning event may be triggered at any time, it maybe periodically triggered when no clogging of the injectors exists.Unnecessary cleanings waste cleaning fluid, thereby increasingoperational cost of the system. And, because cleaning causes isolationof the tested injector, engine operation may be interrupted each time acleaning is initiated.

The cleaning system of the present disclosure solves one or more of theproblems set forth above.

SUMMARY OF THE INVENTION

One aspect of the present disclosure is directed to an injector cleaningsystem. The injector cleaning system may include a supply of injectionfluid and an injector configured to receive and inject the injectionfluid. The injector cleaning system may also include a pressure sensorassociated with the injector to generate a signal indicative of thepressure of the injection fluid supplied to the injector. The injectorcleaning system may further include a controller in communication withthe pressure sensor. The controller may be configured to determine apressure decay rate of injection fluid supplied to the injector during anormal injection event based on the signal. The controller may befurther configured to compare the determined pressure decay rate to anexpected pressure decay rate, and supply cleaning fluid to the injectorbased on the comparison.

In another aspect the present disclosure is directed to a method ofcleaning an injector. The method may include pressurizing an injectionfluid and directing the injection fluid to an injector for subsequentinjection. The method may also include sensing a pressure decay rate ofthe injection fluid during a normal injection event and comparing thesensed pressure decay rate to an expected pressure decay rate. Themethod may further include supplying cleaning fluid to the injectorbased on the comparison.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic and diagrammatic illustration of an exemplarydisclosed power unit; and

FIG. 2 is a flowchart depicting an exemplary method of operating thepower unit of FIG. 1.

DETAILED DESCRIPTION

FIG. 1 illustrates a power unit 10 having a common rail fuel system 12,an injector cleaning system 13 and an auxiliary regeneration device 14.For the purposes of this disclosure, power unit 10 is depicted anddescribed as a four-stroke diesel engine. One skilled in the art willrecognize, however, that power unit 10 may be any other type of internalcombustion engine such as, for example, a gasoline or a gaseousfuel-powered engine. Power unit 10 may include an engine block 16 thatat least partially defines a plurality of combustion chambers (notshown), and a crankshaft 18 rotatable within engine block 16.

Fuel system 12 may be a common rail fuel system that may includecomponents that cooperate to deliver injections of pressurized fuel intoeach of the combustion chambers. Specifically, common rail fuel system12 may include a tank 20 configured to hold a supply of fuel, and a fuelpumping arrangement 22 configured to pressurize the fuel and direct thepressurized fuel to a plurality of fuel injectors (not shown) by way ofa common rail 24. It is further contemplated that fuel system 12 may bea unit injector fuel system that is mechanically or hydraulicallyactuated, or any other applicable fuel system known in the art.

Fuel pumping arrangement 22 may include one or more pumping devices thatfunction to increase the pressure of the fuel and direct one or morepressurized streams of fuel to common rail 24. Fuel pumping arrangement22 may be operably connected to power unit 10 and driven by crankshaft18, via a gear train 26. It is contemplated, however, that fuel pumpingarrangement 22 may alternatively be driven electrically, hydraulically,pneumatically, or in any other appropriate manner. Fuel pumpingarrangement 22 may be connected to common rail 24 by way of a fuel line32. One or more filtering elements 34, such as a primary filter and asecondary filter, may be disposed within fuel line 32 in series relationto remove debris and/or water from the fuel pressurized by fuel pumpingarrangement 22.

Auxiliary regeneration device 14 may be associated with an exhausttreatment device 46. In particular, as exhaust from power unit 10 flowsthrough housing 47 of exhaust treatment device 46, particulate mattermay be removed from the exhaust flow by a wire mesh or ceramic honeycombfiltration media 48. Over time, the particulate matter may build up infiltration media 48 and, if left unchecked, the particulate matterbuildup could be significant enough to restrict, or even block the flowof exhaust through exhaust treatment device 46, allowing forbackpressure within the power unit 10 to increase. An increase in thebackpressure of power unit 10 could reduce the power unit's ability todraw in fresh air, resulting in decreased performance, increased exhausttemperatures and poor fuel consumption.

Auxiliary regeneration device 14 may include components that cooperateto periodically reduce the buildup of particulate matter withinfiltration media 48. These components may include a housing 50, aninjector 52, an igniter 54 and a combustion canister 56. Fuel fromcommon rail fuel system 12 may flow to fuel injector 52, situated inhousing 50. From injector 52, fuel may be injected into combustioncanister 56 and ignited by igniter 54 in order to raise the temperatureof filtration media 48. It is contemplated that auxiliary regenerationdevice 14 may include additional or different components such as, forexample, one or more pilot injectors, additional main injectors, acontroller, a pressure sensor, a temperature sensor, a flow sensor, aflow blocking device and other components known in the art. It isfurther contemplated that a system other than fuel system 12 may provideinjection fluid to regeneration device 14.

Injector 52 may be disposed within housing 50 and connected to fuel line32 by way of a fluid passageway 57 and a main control valve 58. Injector52 may be operable to inject an amount of pressurized fuel intocombustion canister 56 at predetermined timings, fuel pressures and fuelflow rates. The timing of fuel injection may be synchronized withsensory input received from a temperature sensor (not shown), one ormore pressure sensors (not shown), a timer (not shown), or any othersimilar sensory devices such that the injections of fuel substantiallycorrespond with a buildup of particulate matter within filtration media48. For example, fuel may be injected as a pressure of the exhaustflowing through exhaust treatment device 46 exceeds a predeterminedpressure level or a pressure drop across filtration media 48 exceeds apredetermined differential value. Alternatively or additionally, fuelmay be injected as the temperature of the exhaust flowing throughexhaust treatment device 46 exceeds a predetermined value. It iscontemplated that fuel may also be injected on a set periodic basis, inaddition to or regardless of pressure and temperature conditions, ifdesired.

Main control valve 58 may include an electronically controlled valveelement that is a solenoid movable against a spring bias in response toa commanded flow rate from a first position, at which pressurized fuelmay be directed to common rail 24, to a second position, at which fuelmay be directed to auxiliary regeneration device 14. It is contemplatedthat main control valve 58 may alternatively be hydraulically orpneumatically actuated, if desired.

During a normal injection event, control valve 58 may open to directpressurized fuel to flow through fuel injector 52 into combustioncanister 56, and control valve 55 may close to end the injection event.After control valve 55 closes, fuel injector 52 may continue to providefuel to combustion canister 56 until the pressure in fuel line 57 dropsand fuel line 57 is substantially empty. This time period of pressurereduction (i.e. decay period) may vary depending on restriction throughfuel injector 52. For the purposes of this disclosure, a normalinjection event may be considered an event where a primary purpose of aninjector is fulfilled. For example, in most situations, a normalinjection event occurs when fuel is injected by a fuel injector for thepurpose of combusting. In regeneration system 14, a normal injectionevent may be considered one in which fuel is injected by fuel injector52 for the purpose of regenerating exhaust treatment device 48.

During a regeneration event, igniter 54 may facilitate ignition of fuelsprayed from injector 52 into combustion canister 56. For example,igniter 54 may embody a spark plug, and a spark developed across anelectrode (not shown) of the spark plug may ignite the locally richatmosphere creating a flame, which may be jetted or otherwise advancedtoward the trapped particulate matter of filtration media 48. As aresult, the temperature within exhaust treatment device 46 may rise to alevel that causes ignition of the particulate matter, therebyregenerating exhaust treatment device 46.

After the regeneration event, the supply of fuel to injector 56 may beshut off. However, some fuel may remain within fuel injector 52 or fluidpassageway 57. This remaining fuel, when subjected to the harshconditions of the exhaust stream may coke or be partially burned,leaving behind a solid residue that can restrict or even block fuelinjector 52. In addition, it may be possible for particulate matter fromthe exhaust flow to enter and block injector 52. For this reason, it maybe necessary to periodically clean or purge the injector of fuel and/orany built up residue or particulate matter between regeneration events.

Injector cleaning system 13 may be associated with auxiliaryregeneration device 14 and incorporate components that may purgeinjector 52 based on the rate of pressure decay at the end of a normalinjection event. The components of injector cleaning system 13 mayinclude pressure a sensor 60, a controller 62 and a cleaning solutionreservoir 64. A purge passageway 66 may fluidly connect auxiliaryregeneration device 14 to cleaning solution reservoir 64. A check valve68 may be disposed within purge passageway 66 to ensure that fuel andother contaminates are blocked from flowing through purge passageway 66to reservoir 64. The flow of cleaning fluid through purge passageway 66may be controlled by way of a control valve 70 in response to a pressuremeasured by pressure sensor 60.

Pressure sensor 60 may be located upstream of fuel injector 52 and maygenerate a signal indicative of the pressure of the fuel and/or cleaningfluid supplied to injector 52. Controller 62 may communicate withpressure sensor 60 via communication line 72.

Controller 62 may include components such as for example, a memory, asecondary storage device, a processor and any other components forcontrolling injector cleaning system 13. Controller 62 may embody asingle microprocessor or multiple microprocessors that include a meansfor cleaning injector 52 based on a sensed pressure decay rate. Numerousavailable microprocessors can be configured to perform the functions ofcontroller 62. Various other known circuits may be associated withcontroller 62, including power supply circuitry, signal-conditioningcircuitry, solenoid driver circuitry, temperature sensor circuitry,communication circuitry and other appropriate circuitry.

Controller 62 may include one or more maps stored within an internalmemory of controller 62 and may reference these maps to determine anexpected pressure decay rate associated with a normal injection (e.g. aregeneration event) and corresponding to one or more engine operatingparameters. The maps may include, for example, tables, graphs,equations, collections of data, etc. For example, controller 62 maycompare an observed pressure decay rate with a known acceptable pressuredecay rate corresponding to a current operating temperature or enginerotational speed. Controller 62 may calculate a difference between theobserved and expected pressure rates and, based on this difference, maydetermine an amount of restriction within the fuel injector 52.Controller 62 may also contain maps that relate the level of restrictionwithin fuel injector 52 to an amount of cleaning fluid, pressure, flowrate and/or flow duration required to adequately clean clogged fuelinjector 52.

Reservoir 64 may contain a pressurized cleaning fluid capable offlushing and/or dissolving exhaust particulate matter and/or coked fueltrapped within fuel injector 52 by way of fluid passageway 57. Forexample, reservoir 64 may be pressurized to approximately 150 psi withnitrogen gas and contain approximately eight to ten ounces of cleaningfluid for the purpose of removing debris as it passes though fuelinjector 52. The cleaning fluid may, for example, be a low sedimentdegreaser with an operating temperature range of about −40° C. to 95° C.It is further contemplated that injector cleaning system 13 may be anair purge system that may, for example utilize an auxiliary air pump toinject air at approximately 30 psi through fuel injector 52.

FIG. 2 illustrates an exemplary method of operating injector cleaningsystem 13. FIG. 2 will be discussed in detail in the following section.

INDUSTRIAL APPLICABILITY

The injector cleaning system of the present disclosure may be applicableto a variety of injectors and in particular, injectors associated withregeneration devices. The cleaning method of the present disclosure maydetermine whether a restriction exists within an injector at the end ofa normal injection event, quantify the level of restriction and providemultiple levels of cleaning, dependant upon an observed level ofinjector restriction. Furthermore, the injector cleaning system of thepresent disclosure may log a failure in the event of an unsuccessfulcleaning routine. The operation of power unit 10 will now be explained.

Referring to FIG. 1, air and fuel may be drawn into the combustionchambers of power unit 10 for subsequent combustion. Specifically, fuelfrom common rail fuel system 12 may be injected into the combustionchambers of power unit 10, mixed with the air therein, and combusted bypower unit 10 to produce a mechanical work output and an exhaust flow ofhot gases. The exhaust flow may contain a complex mixture of airpollutants composed of gaseous and solid material, which can includeparticulate matter. As this particulate laden exhaust flow is directedfrom the combustion chambers through exhaust treatment device 46,particulate matter may be strained from the exhaust flow by filtrationmedia 48. Over time, the particulate matter may build up in filtrationmedia 48 and, if left unchecked, the buildup could be significant enoughto restrict, or even block the flow of exhaust through exhaust treatmentdevice 46. As indicated above, the restriction of exhaust flow frompower unit 10 may increase the backpressure of power unit 10 and reducethe unit's ability to draw in fresh air, resulting in decreasedperformance of power unit 10, increased exhaust temperatures, and poorfuel consumption.

To prevent the undesired buildup of particulate matter within exhausttreatment device 46, filtration media 48 may be regenerated.Regeneration may be periodic or based on a triggering condition such as,for example, a lapsed time of engine operation, a pressure differentialmeasured across filtration media 48, a temperature of the exhaustflowing from power unit 10, or any other condition known in the art.

To initiate regeneration, injector 52 may be caused to selectively passfuel into exhaust treatment device 46 at a desired rate, pressure and/ortiming (i.e. a normal injection event may be initiated). As an injectionof fuel from injector 52 sprays into exhaust treatment device 46, airmay be mixed with the fuel and the mixture may be ignited. The ignitedflow of fuel and air may then raise the temperature of the particulatematter trapped within filtration media 48 to the combustion level of theentrapped particulate matter, burning away the particulate matter and,thereby, regenerating filtration media 48.

Between regeneration events, fuel injector 52 may be selectively purgedof fuel and/or contaminates to ensure proper operation of fuel injector52. Referring to FIG. 1 and FIG. 2, injector cleaning system 13 mayperform a predetermined routine in response to a pressure decay rate atthe conclusion of a regeneration event (e.g. a normal injection event).For example, control valve 58 may open to allow a finite amount of fuelto flow through fluid passageway 57, into injector 52, therebyinitiating a regeneration combustion event within combustion canister 56(step 1). At a predetermined time, control valve 58 may close to blockfurther flow of fuel through fuel line 57 and injector 52, therebyending the regeneration event. However, fuel within fuel line 57 maystill be somewhat pressurized, and thus, the fuel may continue to flowthrough injector 52 until the pressure within fuel line 57 hasdiminished. During the interval in which fuel is forced from fuel line57 and no additional fuel is supplied to fuel line 57, the pressurewithin fuel line 57 may decay at a rate corresponding to the rate atwhich fuel injector 52 injects fuel into combustion canister 56. Thedecay rates for each normal injection event may be relatively constant.However, if the flow of fuel through fuel injector 52 is restricted, therate at which the pressure within fuel line 57 decays may decrease. Thepressure in fluid passageway 57 may be measured by pressure sensor 60during the pressure decay interval, and controller 62 may calculate apressure decay rate based on the pressure measurements communicated viacommunication line 72 (step 2).

Controller 62 may compare the observed decay rate to an expectedpressure decay rate (corresponding to a substantially clog-freeinjector) stored in one of its maps. In order to determine whetherinjector 52 is clogged, controller 62 may access a map that may includemultiple maps indexed according to an engine operating parameter.Controller 62 may compare the observed pressure decay rate to anexpected pressure decay rate stored in a map corresponding to a currentengine operating parameter. If the observed pressure decay rate iscomparable or greater than the expected pressure decay rate theregeneration event may proceed as normal. However, if the observedpressure decay rate is lower than the expected pressure decay rate,injector 52 may be at least partially clogged (step 3).

Following an observation of a lower than expected decay rate, controller62 may open control valve 70, allowing the passage of cleaning solutionfrom reservoir 64 into auxiliary regeneration device 14 for purgingand/or combustion purposes (step 4). Controller 62 may calculate themagnitude of the injector restriction, based on the difference betweenthe expected pressure decay rate and the observed pressure decay rate,in order to determine a quantity of cleaning fluid required to removethe clog, as well as the pressure, flow rate and/or duration of thefluid release. For example, controller 62 may trigger control valve 70to release anywhere between about one half and three ounces of cleaningsolution, based on the injector restriction amount. It is furthercontemplated that the pressure, flow rate and the duration of theinjection of the cleaning fluid may be dependant upon the pressure decayrate. Alternately or additionally, controller 62 may direct the cleaningfluid to mix with fuel during the injector cleaning event. Furthermore,it is considered that pressurized fuel may be directed into fuel line 57to drive the cleaning fluid into injector 52.

After the required amount of cleaning fluid has been released, controlvalve 70 may close. During the period in which cleaning fluid is beingdrained from fluid passageway 57 (also called a cleaning check period)and injected by fuel injector 52, pressure sensor 60 may againcommunicate the pressure within fluid passageway 57 to controller 62,and controller 62 may make a second comparison of the calculatedpressure decay rate to the expected pressure decay rate (step 5).Alternatively or additionally, fuel may be injected during the cleaningcheck period (i.e. after the cleaning), with or without initiatingcombustion, for the purposes of detecting the resulting pressure decayrate.

When the second observed pressure decay rate exceeds the expectedpressure decay rate, controller 62 may be allowed to initiate asubsequent purging event in a similar manner (step 6). However, if thepressure decay rate observed at the end of the second purging eventstill exceeds the expected pressure decay rate (step 7), controller 62may log a fault indicating a severely clogged fuel injector 52 and mayprevent initiation of additional purging events (step 8).

Several advantages may be associated with the injector cleaning systemof the present disclosure. Specifically, the disclosed system may allowfor the detection of a restricted injector following each normalinjection event. That is, detection of a restriction may occur duringevery normal injector operation, without requiring additional or specialinjections. The injector cleaning system of the present disclosure maydetect such a restriction within an injector without operator initiationand may continuously check for clogging, ensuring that the injector maycontinuously operate at an optimal level. Furthermore, the disclosedinjector cleaning system may inject a quantity of cleaning fluid basedon the severity of a restriction, thereby ensuring efficient use ofcleaning fluid. Additionally, the disclosed injector cleaning system maymeasure the effectiveness of each cleaning event and either initiate asecond cleaning event or log a failure. In this manner, the disclosedinjector cleaning system may ensure that either the injectors remainclean and unrestricted, or an operator is alerted to sub-optimaloperations.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the injector cleaning systemof the present disclosure without departing from the scope of thedisclosure. Other embodiments will be apparent to those skilled in theart from consideration of the specification and practice of the injectorcleaning system disclosed herein. It is intended that the specificationand examples be considered as exemplary only, with a true scope of thedisclosure being indicated by the following claims and theirequivalents.

1. An injector cleaning system, comprising: a supply of injection fluid;an injector configured to receive and inject the injection fluid; apressure sensor associated with the injector to generate a signalindicative of the pressure of the injection fluid supplied to theinjector; and a controller in communication with the injector and thepressure sensor, the controller being configured to: determine apressure decay rate of injection fluid supplied to the injector during anormal injection event based on the signal; compare the determinedpressure decay rate to an expected pressure decay rate; and supplycleaning fluid to the injector based on the comparison.
 2. The injectorcleaning system of claim 1, wherein supplying cleaning fluid initiates acleaning event and the controller is further configured to determine asecond pressure decay rate following every cleaning event to determinean effectiveness of the cleaning event.
 3. The injector cleaning systemof claim 2, wherein a supplemental injection event is initiated fordetermination of the second pressure decay rate.
 4. The injectorcleaning system of claim 3, wherein injection fluid associated with thesupplemental injection event passes from the injector through anassociated combustion chamber without combustion.
 5. The injectorcleaning system of claim 2, wherein the controller is further configuredto initiate a secondary cleaning event when the second pressure decayrate exceeds the expected pressure decay rate by a predetermined amount.6. The injector cleaning system of claim 5, wherein the controller isfurther configured to determine a third pressure decay rate followingthe secondary cleaning event and log a fault condition when the thirdpressure decay rate exceeds the expected decay rate by a predeterminedamount.
 7. The injector cleaning system of claim 1, wherein thecontroller is configured to determine the pressure decay rate duringevery normal injection event.
 8. The injector cleaning system of claim1, wherein the controller includes at least one map stored in memorythereof relating the comparison to an injector restriction amount, andthe amount of cleaning fluid supplied to the injector is based on theinjector restriction amount.
 9. The injector cleaning system of claim 8,wherein the at least one map includes a plurality of maps, each of theplurality of maps being indexed accordingly to an engine operationalparameter.
 10. The injector cleaning system of claim 1, whereinsupplying includes directing the cleaning fluid to mix with theinjecting fluid upstream of the injector.
 11. The injector controlsystem of claim 1, wherein the injector is located to inject theinjection fluid into an exhaust stream to raise a temperature of theexhaust stream.
 12. A method of cleaning, comprising: pressurizing aninjection fluid; injecting the pressurized injection fluid during anormal injection event; sensing a pressure decay rate associated withthe normal injection event; comparing the sensed pressure decay rate toan expected pressure decay rate; and injecting a cleaning fluid based onthe comparison.
 13. The method of claim 12, wherein injecting thecleaning fluid initiates a cleaning event and the method furtherincludes determining a second pressure decay rate following everycleaning event to determine an effectiveness of the cleaning event. 14.The method of claim 13, further including initiating a supplementalinjection event is initiated for determination of the second pressuredecay rate.
 15. The method of claim 13, further including initiating asecondary cleaning event when the second pressure decay rate exceeds theexpected pressure decay rate by a predetermined amount.
 16. The methodof claim 15, further including determining a third pressure decay ratefollowing the secondary cleaning event and logging a fault conditionwhen the third pressure decay rate exceeds the expected decay rate by apredetermined amount.
 17. The method of claim 12, wherein sensing thepressure decay rate includes sensing the pressure decay rate duringevery normal injection event.
 18. The method of claim 12, furtherincluding relating the comparison to a restriction amount, wherein anamount of cleaning fluid injected is based on the restriction amount.19. The method of claim 12, wherein injecting the cleaning fluidincludes directing the cleaning fluid to mix with the injecting fluidprior to injection.
 20. An exhaust treatment system, comprising: asupply of injection fluid; a sensor associated with the supply ofinjection fluid to generate a signal indicative of an injection fluidpressure; a housing configured to receive a flow of exhaust; an injectordisposed within the housing to receive the supply of injection fluid andinject the injection fluid into the flow of exhaust; a supply ofcleaning fluid; and a controller in communication with the sensor andthe injector, the controller being configured to: determine a pressuredecay rate of injection fluid supplied to the injector during a normalinjection event based on the signal; compare the determined pressuredecay rate to an expected pressure decay rate; and supply cleaning fluidto the injector in an amount based on the comparison.